1. Field of the Invention
This invention relates to a forced cooling casting apparatus for causing directional solidification by use of a cooling medium.
2. Description of the Related Art
Various measures for rapidly cooling a molten metal or for causing directional solidification have been employed in the past in order to produce castings made of an aluminum alloy or the like without casting defects resulting from casting processes. For instance, water cooling and air cooling have been used primarily in a gravitational casting method and a low pressure casting method in order to promote the solidification of the molten metal. In accordance with these conventional cooling methods, however, supercooling of the molten metal is likely to occur so that an inferior run is likely to occur at the time of pouring the molten metal or a mold temperature changes periodically during a casting cycle. As a result, a high level of skill is necessary to control the mold temperature, or a casting apparatus becomes complicated in construction and requires a higher cost of production.
To eliminate the problem described above, there has been proposed a direct cooling type casting method (Japanese Published Patent Application No. 109559/1982) which can accomplish efficiently and rapidly the intended directional solidification and can provide excellent castings free from any defects and having high mechanical strength without being limited by the dimension and size of castings. This technique provides the excellent effects that the casting cycle can be shortened and the mechanical strength of the resulting castings can be improved.
In accordance with the method described above, however, sufficient directional solidification cannot be obtained from time to time when the size of intended castings is as large as a cylinder head of a car. For this reason, the applicants proposed a forced cooling type casting method which improves directional solidification by incorporating tubular members in a cavity for products and passing a cooling medium through the tubular members (Japanese Published Patent Application No. 86966/1983. See also U.S. patent application Ser. No. 814,929, filed on Dec. 30, 1985 and U.S. patent application Ser. No. 853,722 having the same filing date as the present application and entitled "FORCED COOLING CONTINUOUS CASTING APPARATUS", the subject matter of both of which is incorporated herein by reference.)
Recently, a cooling method has been developed which divides the period from a molten metal charging step to a complete solidification of products into a plurality of stations and cools the products step-wise in order to fulfill the requirements for a shorter casting cycle due to an increasing dimension of castings, and in order to improve producibility. According to this method, a casting apparatus is conveyed as a whole on a track by rollers and is subjected to the cooling step at each station.
However, the following disadvantages occur in accordance with the technique described above.
In order to rapidly cause suitable directional solidification while taking into consideration the shape of large castings when casting them, a plurality of tubular members must be incorporated into the casting and at the same time, a plurality of cooling medium feeders must also be disposed in order to pass a cooling medium such as water through the tubular members. Therefore, the system becomes more complicated in construction, and must be disposed at each station. Thus, the overall system becomes larger and more expensive.